Laminates with adhesive layer of white-pigmented, melt-stable ethylene/carboxylic acid copolymer compositions

ABSTRACT

A laminated structure comprising at least two nonadhesive layers and at least one white-pigmented adhesive layer, wherein the white-pigmented adhesive layer is made of a composition stabilized against thermal crosslinking and consequent reduction of its melt index, consisting essentially of a uniform dispersion of alumina-coated titanium dioxide pigment in a blend of a matrix polymer which is a dipolymer of ethylene with an ethylenically unsaturated carboxylic acid or a terpolymer of ethylene with an ethylenically unsaturated carboxylic acid and with another ethylenically unsaturated comonomer, or with carbon dioxide or sulfur dioxide, with a stabilizing polymer which is a high melt index copolymer of ethylene with acrylic or methacrylic acid. Such laminated structures include, for example, toothpaste tubes, condiment pouches, traffic road signs, and roadway lane marking tapes.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of my application Ser. No. 07/436,467filed Nov. 14, 1989, and now allowed as U.S. Pat. No. 4,992,486.

BACKGROUND OF THE INVENTION

This invention relates to laminated structures in which at least oneadhesive layer is a melt-stable, titanium dioxide-containing compositionof one or more copolymers of ethylene with alpha, beta-unsaturatedcarboxylic acids such as, e.g., toothpaste tubes, where metal foil islaminated to a printable plastic layer on which the name of the productor other similar information is to be printed. Ethylene copolymers withalpha, beta-unsaturated carboxylic acids are known to be very good hotmelt adhesives, which are suitable for bonding the outer layer to themetal foil or to another plastic layer. When the outer layer is a clearor at least translucent plastic, it is considered advantageous from thestandpoint of aesthetics and commercial appeal that the adhesive layerbe white-pigmented, so that the white color may show through. Anothertypical application for such white-pigments copolymers is in condimentpouches.

Traditionally, titanium dioxide has been used as white pigment forplastics and for other purposes. However, commercial titanium dioxideparticles normally are coated on their surface with alumina, whichimproves the pigment's flowability. When such alumina-coated titaniumdioxide is incorporated into an ethylene/alpha, beta-unsaturatedcarboxylic acid copolymer, and such pigmented copolymer is exposed tohigh temperatures, such, for example, as are encountered duringextrusion, the copolymer appears to be reacting with the aluminacoating, as evidenced by a decrease of the polymer's melt index. Furtherreduction of melt index occurs on storage. Such lowering of the meltindex is undesirable because it leads to nonuniform coating thicknessesand pinholes in the coatings. In addition to the instability of the meltindex, a further problem has been the formation of gels in the polymer,resulting in poor quality extrusion coatings.

There is, therefore, a great need for a thermally stable titaniumdioxide-pigmented ethylene/alpha, beta-unsaturated carboxylic acidcopolymer.

SUMMARY OF THE INVENTION

According to this invention, there is provided a laminate structurecomprising at least two nonadhesive layers and at least onewhite-pigmented adhesive layer, which adhesive layer is made of acomposition stabilized against thermal crosslinking and consequentdecrease of its melt index consisting essentially of a uniformdispersion of alumina-coated titanium dioxide pigment in a blend of amatrix polymer with a stabilizing polymer,

the matrix polymer being a copolymer represented by the formula E/X/Y,where E stands for ethylene; X stands for a C₃ -C₇ alpha,beta-unsaturated carboxylic acid; and Y, which is optional, stands foranother copolymerizable comonomer selected from the group consisting ofC₃ -C₇ alpha, beta-unsaturated carboxylic acids, C₁ -C₁₀ alkyl esters ofsuch acids, vinyl esters, vinyl ethers, acrylonitrile,methacrylonitrile, carbon monoxide, and sulfur dioxide; the respectiverelative weight ratios of the monomers in said E/X/Y copolymer beingabout 96:4:0 to 40:30:30, and the melt index of said copolymer,determined according to ASTM D1238, Condition E, being about 0.1-100dg/min; and

the stabilizing polymer being a high melt index copolymer of ethylenewith an unsaturated carboxylic acid selected from the group consistingof acrylic acid (E/AA copolymer) and methacrylic acid (E/MAA copolymer),said high melt index copolymer having a melt index of at least about5,000 dg/min, but preferably at least 10,000 dg/min, determinedaccording to ASTM D1238, condition E, and containing at least about 5weight percent, preferably at least 9 weight percent, of carboxylic acidmonomer;

the relative weight ratio of matrix polymer to stabilizing polymer beingabout 95:5 to 80:20, and the amount of titanium dioxide in the blendbeing about 5 to 20 weight percent.

The composition may be further compounded to incorporate minor amountsof conventional additives such as, e.g., stabilizers, antioxidants, andslip improving agents. It can be additionally formulated with furtheradditives such as, for example, plasticizers and unreactive fireretardants such as halogenated hydrocarbons, the total amount ofplasticizers, if present, being no more than about 15 weight percent,but preferably 5-15 weight percent of the final composition; and theamount of fire retardants, if any, being about 10 to 30 weight percentof the final composition, depending on the level of fire resistancedesired.

BRIEF DESCRIPTION OF THE DRAWING

The drawing represents a plot of intitial melt index of representativecompositions of the present invention as well as of some compositionsoutside the scope of the present invention vs. weight percent of highmelt index copolymer in those compositions.

DETAILED DESCRIPTION OF THE INVENTION

Definition: For the purpose of the present disclosure and claims, theexpression "consisting essentially of" means that the recited componentsare essential, while smaller amounts of other components may be presentto the extent that they do not detract from the operability of thepresent invention.

The E/X/Y copolymers suitable in the compositions of the presentinvention either are available commercially or can be made according toknown processes from readily available monomers. Copolymers of ethylenewith unsaturated carboxylic acids are described in U.S. Pat. Nos.4,351,931 to Armitage, 4,252,954 to Chatterjee, 3,264,272 to Rees,3,520,861 to Thomson et al., 3,884,857 to Ballard et al., and 3,658,741to Knutson et al. Terpolymers of ethylene with unsaturated carboxylicacids and with alkyl esters of unsaturated carboxylic acids aredescribed in U.S. Pat. No. 3,264,272 to Rees; terpolymers of ethylenewith carbon monoxide and unsaturated carboxylic acids are disclosed inU.S. Pat. No. 3,780,140 to Hammer, while terpolymers with sulfur dioxideand unsaturated carboxylic acids are described in U.S. Pat. No.3,784,140 to Hammer. Various ethylene copolymers with methacrylic acidare sold by E. I. du Pont de Nemours and Company under the trademarkNUCREL®. Ethylene copolymers with acrylic acid are sold by Dow ChemicalCompany under the trademark Primacor®. Carboxylic acids, in addition toacrylic, methacrylic, and higher unsaturated monocarboxylic acids, alsoinclude monoesters of alpha, beta-unsaturated dicarboxylic acids suchas, e.g., maleic, fumaric, and itaconic acids. Typical alkyl esters ofalpha, beta-unsaturated carboxylic acids include methyl, ethyl, butyl,pentyl, hexyl, octyl, and decyl esters, both linear and branched, aswell as diesters of dicarboxylic acids.

High melt index copolymers of ethylene with acrylic or methacrylic acidnormally will be dipolymers, although a minor amount of a third monomer,such as, for example, one of those that can be present in matrixterpolymers, can be tolerated without impairing the operability of thisinvention.

High melt index copolymers of ethylene with acrylic acid are available,for example, from Allied Signal Corporation under the trademark A-C®Copolymers. Such copolymers also can be made according to known methods,as illustrated by means of examples herein.

High melt index copolymers of ethylene with methacrylic acid also can bemade according to known methods, as illustrated by means of examplesherein.

Titanium dioxide is available from several sources, including E. I. duPont de Nemours and Company.

Preferred matrix dipolymers are dipolymers of ethylene with methacrylicacid (X is methacrylic acid and Y is absent) and especially those inwhich the weight proportion of methacrylic acid is about 3-30%,preferably 4-15% by weight. Preferred matrix terpolymers are terpolymersof ethylene in which X is methacrylic acid and Y is vinyl acetate,n-butyl acrylate, or isobutyl acrylate.

It is generally preferred to choose the type and amount of thestabilizing polymer such that the resulting initial melt index of thecomposition is close to the melt index of the matrix polymer itself. Aswill be seen below, this objective can be met for the preferredcompositions with moderate amounts, 15% or less, of stabilizing polymer.

Laminates of the present invention comprise a substrate, for example,metal foil, sheet of plastic, or sheet of kraft paper, at least oneadhesive layer, and at least one additional layer, wherein a compositionof the present invention serves as the bonding agent. Such laminates canbe made in a number of ways, all of which are generally known to theart, such as, for example, film casting, multilayer blow molding,compression molding, coextrusion, and extrusion lamination. In makingthese laminates, the stabilized, titanium dioxide-containing composition(sometimes also identified hereinafter as WPAC, which stands for whitepigmented acid copolymer) will normally be provided in one of two forms:either it is first formed into a sheet by blown film extrusion orcalendering, and then, in a second step, the sheet is rolled and pressedonto a polymer substrate; or it is supplied in a particulate form suchas pellets or the like, which are extruded into a sheet in contact withvarious substrate layers.

Film casting is a continuous process by which a thermoplastic materialis extruded through a slot die onto a chill roll, where it is quenchedand solidified. The molten film normally exits the extruder verticallythrough a slot die and tangentially contacts the chill roll that coolsthe material into a web. Extrusion lamination is an adaptation of thistechnique, wherein the film is cast onto a substrate such as kraftpaper, aluminum foil, polyester film, or low density polyethylene (LDPE)film. Since the WPAC compositions of the present invention normally areused as adhesive or bonding layers in laminate structures, the WPAC filmis cast between two substrates. A typical laminate may thus be, forexample, aluminum foil//WPAC//clear LDPE or kraft paper//WPAC//clearLDPE. In a multilayer laminate structure, more than one WPAC bondinglayers may be present.

Another common process for producing films of thermoplastic materials isblown film extrusion. In this process, a molten tube of polymer issimultaneously drawn axially and expanded radially from an annular slitdie. The hot tube is cooled by high velocity air from an air ring on theoutside and sometimes also on the inside of the tube. Normally, the tubeis formed and drawn in a vertical and upward direction.

In multilayer blow molding, multilayer laminate structures are formedthrough coextrusion. A multiplicity of extruders, usually from two toseven, feed individual polymers into a coextrusion head, where amultilayer laminate is extruded. This may be a flat film or sheetlaminate or a hollow tube (parison). The parison is captured at regularintervals in vertically positioned molds. Thereafter, the hot plasticmaterial is blown with air to expand it to the configuration of the moldcavity, thus forming the final, usually container, shape. Thecontinually extruded parison is cut during the process. The WPACcompositions of this invention can be used as the adhesive layer instructures such as, for example, ethylene/vinyl alcoholcopolymer//WPAC//high density polyethylene or polypropylene.

Compression molding is the simplest process for producing laminates. Theapparatus, or molding press, consists of two platens that closetogether. Heat and pressure are applied to form the material into thedesired shape. A typical laminate that can be made in such equipment hasthe following layers: aluminum foil//WPAC//clear polyester. The twoouter layers are higher melting than the inner layer, so that under thepress conditions only the adhesive inner layer is activated. A typicalpress temperature is about 200° C. Compression force can reach as muchas 1000 tons.

Laminates in sheet or film form can be used for making a variety ofarticles such as, for example, the aforementioned toothpaste tubes, andcondiment pouches, where the substrate is either metal foil or a plasticsheet, and the top coat is clear plastic on which appropriateinformation is printed; traffic road signs, where the substrate iseither plastic or metal, and the top coat is clear plastic; and roadwaylane marking tapes, in which both the bottom layer and the top layer aremade of plastics. Other types of laminated articles, which can be formeddirectly, for example, by compression molding or by coextrusion and blowmolding, comprise containers of various types, including bottles.

In the practical operation of the present invention, the high melt indexstabilizing polymer and titanium dioxide may first be blended in asuitable equipment above the melt temperature of the polymer to form amasterbatch containing about 50-75 weight percent of TiO₂ uniformlydispersed in the polymer matrix. This masterbatch is then againmelt-blended in the desired proportions with the matrix polymer. As analternative, all three components may be melt-blended in one step.Neither method appears to offer an advantage over the other.

This invention is now illustrated by the following examples of certainpreferred embodiments thereof, where all parts, proportions, andpercentages are by weight unless otherwise indicated. TiO₂ used in allthe examples was a commercial product of E. I. du Pont de Nemours andCompany sold under the trademark Ti-Pure® R101. It had an averageparticle size of 0.18 micrometer and was coated on its surface withaluminum oxide.

Small quantities of material, about 50 g, were melt-compounded using aHaake System 40 Mixer fitted with roller-blade rotors. Samples wereprepared for this mixer by dry blending the various powders and pelletsand charging the total slowly to the mixer. Unless otherwise noted, thecompounds were mixed in the Haake mixer at the required temperature for3 minutes at 15 RPM, then for 7 minutes at 50 RPM.

Larger quantities of dry blend were compounded on a Werner andPfleiderer corotating twin screw extruder using either a 28 mm trilobalor a 30 mm bilobal screw configuration.

Melt Index (MI)

Unless otherwise specified, melt index was determined, according to ASTMD1238, condition E, which requires a temperature of 190° C. and a 2,160g weight.

High MI Copolymers

High MI acid copolymers E through M were prepared according to thegeneral disclosure of U.S. Pat. No. 3,264,272 to Rees. Commercialethylene and acrylic acid (AA) or methacrylic acid (MAA) were fed in acontinuous manner to a stirred pressure vessel. Free radical initiator(t-butyl peroxyacetate) was fed by a separate line. The flow of monomerswas adjusted to give constant mole ratios, and the feed rate was thesame as the rate of discharge of polymer and of unpolymerized monomersfrom the reactor. A small amount of acetone or methanol, used as atelogen (chain transfer agent), was also introduced into the reactorwith the feed monomers to control the molecular weight.

Table I represents the state of the art of compounding pigmentedcompositions containing TiO₂ and gives melt index stability data forrepresentative compositions containing an E/MAA copolymer as the matrixpolymer and a commercial dispersion of titanium dioxide in either anethylene/methyl acrylate copolymer carrier or a low density polyethylene(LDPE) carrier, both supplied by Ampacet Co. of Mount Vernon, Illinois.Samples 1-3 were the matrix polymers, and samples 4 and 5 were theAmpacet TiO₂ concentrates. Samples 6 through 11 were made byextruder-blending 25 parts of Ampacet concentrate with 75 parts ofmatrix polymer at 170° C. The resulting blends had initial MIs of 11.0to 5.4, but those dropped considerably after mixing at 280° C. in theHaake Mixer. Samples 13 and 14 were made by directly compounding 30parts of Ampacet concentrates with 70 parts of matrix polymer in theHaake Mixer. The blends had very low MIs, suggesting a rather highdegree of crosslinking. Sample 12 was a control, made by direct blendingof matrix polymer with TiO₂. This sample had a higher MI than samples 13and 14, which were made via the concentrates.

                                      TABLE I                                     __________________________________________________________________________    STATE OF THE ART OF POLYMER/TIO.sub.2 COMPOUNDING                                 TiO.sub.2                                                                            Matrix                                                                              % TiO.sub.2                                                                        Extruder                                                                              Haake                                           Sample                                                                            Dispers.,                                                                            Polymer,                                                                            in   Mix     Mix MI                                          No. Polymer, %                                                                           %     Blend                                                                              Temp.                                                                              MI Temp.                                                                             Init.                                                                            1 Mo.                                                                             2 Mo.                                __________________________________________________________________________    1   --     [a],                                                                             100                                                                              --   --   12.5                                                                             --  -- --  --                                   2   --     [b],                                                                             100                                                                              --   --   9.1                                                                              --  -- --  --                                   3   --     [c],                                                                             100                                                                              --   --   7.0                                                                              --  -- --  --                                   4   [d],                                                                             100 --    --   --   9.1                                                                              --  -- --  --                                   5   [e],                                                                             100 --    --   --   5.1                                                                              --  -- --  --                                   6   [d],                                                                             25  [a],                                                                             75 12.5 170  11.0                                                                             280 0.4                                                                              0.6 0.5                                  7   [d],                                                                             25  [b],                                                                             75 12.5 170  9.7                                                                              280 2.0                                                                              2.0 2.0                                  8   [d],                                                                             25  [c],                                                                             75 12.5 170  7.1                                                                              280 0.8                                                                              0.8 0.8                                  9   [e],                                                                             25  [a],                                                                             75 12.5 170  9.1                                                                              280 0.7                                                                              0.8 0.6                                  10  [e],                                                                             25  [b],                                                                             75 12.5 170  7.7                                                                              280 2.1                                                                              2.1 2.7                                  11  [e],                                                                             25  [c],                                                                             75 12.5 170  5.4                                                                              280 0.7                                                                              0.8 0.6                                  12  --     [a],                                                                             85 15.0 --   -- 280 1.2                                                                              1.5 1.4                                  13  [e],                                                                             30  [a],                                                                             70 15.0 --   -- 280 1.0                                                                              0.8 0.7                                  14  [d],                                                                             30  [a],                                                                             70 15.0 --   -- 280 0.4                                                                              0.5 0.5                                  __________________________________________________________________________     [a] E/MAA copolymer, 9% MMA, nominal MI = 10                                  [b] E/MAA copolymer, 6% MAA, nominal MI = 9                                   [c] E/MAA copolymer, 4% MAA, nominal MI = 7                                   [d] "Ampacet" 11892: 50% TiO.sub.2, E/Methyl acrylate carrier, nominal        blend MI = 12                                                                 [e] "Ampacet"  11171: 50% TiO.sub.2, LDPE carrier, nominal blend MI = 5  

Tables II and III describe the various copolymers used in the course ofthe experimental work reported herein.

Table II lists the matrix copolymers, and Table III lists the high meltindex stabilizing E/AA and E/MAA copolymers. The matrix copolymers areidentified by Roman numerals I through IV. High melt index stabilizingcopolymers are designated by letters A-G. Those designated H and J-Phave melt indices below 5,000 dg/min and are outside the scope of thepresent invention; they are included for comparison purposes only. Gelpermeation chromatography data reported in Table III were obtained usingWaters HPLC 150, AT-80M/S columns Numbers 7J732 and 7G707, withtrichlorobenzene as solvent, at a temperature of 135° C. The intrinsicviscosities were calculated using the Mark-Houwink equation withk=0.0004340 and alpha=0.724.

                  TABLE II                                                        ______________________________________                                        ETHYLENE/METHACRYLIC                                                          ACID MATRIX COPOLYMERS                                                                          I    II                                                     ______________________________________                                        Acid Content (%)    9.0    4.0                                                Melt Index (dg/min) 10     11                                                 ______________________________________                                    

                                      TABLE III                                   __________________________________________________________________________    HIGH MI COPOLYMERS                                                            __________________________________________________________________________              A*   B*   C*   D*   E   F                                           __________________________________________________________________________    Acid Type AA   AA   AA   AA   MAA AA                                          Acid Content (%)**                                                                      5.0  9.1  15.6 23.8 22.0                                                                              18.1                                        Meq/g     0.69 1.26 2.17 3.31 2.59                                                                              2.51                                        Melt Index                                                                    Literature                                                                              >15,000                                                                            >15,000                                                                            >15,000                                                                            >15,000                                                                            --  --                                          Determined                                                                              --   --   --   --   12200                                                                             >10000                                      GPC Data                                                                      Peak MW   8160 6850 4590 1800 3130                                                                              2740                                        Mw        10400                                                                              8820 5670 2860 3720                                                                              3190                                        Mv        9610 8040 5100 2460 3360                                                                              2900                                        Mn        5470 3420 2040 960  1450                                                                              1330                                        Mw/Mn     1.90 2.58 2.78 2.97 2.56                                                                              2.41                                        Intr. Visc.                                                                             0.16 0.155                                                                              0.115                                                                              0.124                                                                              0.155                                                                             0.139                                       __________________________________________________________________________              G   H  J  K  L   M   N   P                                          __________________________________________________________________________    Acid Type AA  AA AA AA MAA MAA MAA MAA                                        Acid Content (%)**                                                                      29.7                                                                              18.1                                                                             24.5                                                                             29.5                                                                             22.4                                                                              28.6                                                                              34.6                                                                              11.0                                       Meq/g     4.13                                                                              2.51                                                                             3.40                                                                             4.10                                                                             2.64                                                                              3.36                                                                              4.07                                                                              1.29                                       Melt Index                                                                    Literature                                                                              --  -- -- -- --  --  --  100                                        Determined                                                                              10000                                                                             2400                                                                             1750                                                                             1200                                                                             1120                                                                              1000                                                                              1100                                                                              --                                          GPC Data                                                                     Peak MW   2350                                                                              7720                                                                             6910                                                                             5210                                                                             7850                                                                              6850                                                                              4170                                                                              N/D                                        Mw        3120                                                                              9800                                                                             8210                                                                             6420                                                                             9950                                                                              7690                                                                              5660                                                                              N/D                                        Mv        2810                                                                              8870                                                                             7360                                                                             5760                                                                             8960                                                                              6940                                                                              5040                                                                              N/D                                        Mn        1200                                                                              3480                                                                             2730                                                                             2090                                                                             3570                                                                              2690                                                                              1890                                                                              N/D                                        Mw/Mn     2.60                                                                              2.82                                                                             3.01                                                                             3.07                                                                             2.79                                                                              2.86                                                                              2.99                                                                              N/D                                        Intr. Visc.                                                                             0.136                                                                             0.313                                                                            0.274                                                                            0.229                                                                            0.315                                                                             0.262                                                                             0.208                                                                             N/D                                        __________________________________________________________________________     *"A-C" resins from AlliedSignal Co.                                           **By titration                                                           

Table IV lists representative pigmented compositions obtained frommatrix polymer I by compounding at 280° C. with varying amounts of highMI copolymers. Samples 15-18, 33, and 41 were controls containing nohigh MI copolymer. Samples 15-32 contained 15% of TiO_(2;) samples 33-40contained 9% of TiO₂ ; and samples 41-42 contained 8% of TiO₂. Samples38-40 are outside the scope of the invention. These data show that withincreasing level of high MI copolymer the initial MI increased, and MIstability improved.

                                      TABLE IV                                    __________________________________________________________________________    PIGMENTED COMPOSITIONS BASED ON                                               MATRIX POLYMER I COMPOUNDED AT 280° C.                                 High MI       Matrix    MI                                                    Sample No.                                                                          Copolymer, %                                                                          Polymer, %                                                                           TiO.sub.2                                                                        Initial                                                                           2 Wk.                                                                             1 Mo.                                                                             2 Mo.                                     __________________________________________________________________________    15    --      85     15 2.5 2.4 2.7 2.3                                       16    --      85     15 1.4 1.5 1.3 1.3                                       17    --      85     15 1.4 --  --  --                                        18    --      85     15 1.6 1.8 --  --                                        19    A,  2   83     15 2.2 2.7 2.2 2.2                                       20    A,  5   80     15 2.2 2.7 2.6 2.7                                       21    A,  10  75     15 4.1 4.4 4.0 3.2                                       22    A,  15  70     15 8.2 7.3 7.0 6.7                                       23    B,  2   83     15 1.6 1.6 1.6 1.5                                       24    B,  5   80     15 2.1 2.2 2.7 1.8                                       25    B,  10  75     15 5.1 5.5 4.9 5.2                                       26    B,  15  70     15 9.1 10.0                                                                              8.6 9.0                                       27    C,  2   83     15 2.2 2.4 2.7 2.4                                       28    C,  5   80     15 3.1 3.9 3.4 3.8                                       29    C,  7.5 77.5   15 6.0 6.4 6.0 --                                        30    C,  10  75     15 7.6 8.0 7.0 7.7                                       31    C,  10  75     15 7.9 8.8 --  --                                        32    C,  15  70     15 16.4                                                                              --  15.4                                                                              15.1                                      33    --      91     9  4.1 4.0 3.9 4.1                                       34    C,  3   88     9  5.7 6.2 6.2 6.8                                       35    C,  5   86     9  6.4 6.9 7.9 8.7                                       36    C,  8   83     9  11.5                                                                              11.5                                                                              12.1                                                                              10.8                                      37    C,  10  81     9  14.0                                                                              14.9                                                                              15.0                                                                              12.2                                      38    P,  5   86     9  4.9 5.2 5.5 5.3                                       39    P,  10  81     9  5.8 5.6 6.2 6.6                                       40    P,  15  76     9  6.0 6.1 6.5 5.3                                       41    --      92     8  3.7 4.1 --  4.2                                       42    C,  4   88     8  7.1 7.2 --  7.0                                       __________________________________________________________________________

Table V similarly lists representative pigmented compositions obtainedfrom matrix polymer II. Here, samples 43-55 contained 15% of TiO₂ ;samples 56-63 contained 9% of TiO₂ ; and samples 64-69 contained 6% ofTiO₂. Samples 43 and 56 were controls. The same general observation canbe made that a higher level of high MI copolymer increased both the MIand the MI stability of the pigmented compositions.

The drawing is a plot comparing the effectiveness of representative highMI copolymers in increasing the initial MI of TiO₂ -containing matrixpolymer II compositions. It shows the superiority of copolymers B and C,which had MI's in excess of 15,000, over copolymers H, J, K, L, and M,which had MI's from 2400 to 1000. The melt indices of the compositionscontaining copolymers B and C were higher initially and increaseddramatically with the level of the copolymers B or C, while they werelower initially for copolymers H through L and either increased to amuch lesser degree or not at all with increasing levels of thosecopolymers.

                                      TABLE V                                     __________________________________________________________________________    PIGMENTED COMPOSITIONS CONTAINING                                             MATRIX POLYMER II COMPOUNDED AT 280° C.                                High MI       Matrix    MI                                                    Sample No.                                                                          Copolymer, %                                                                          Polymer, %                                                                           TiO.sub.2                                                                        Initial                                                                           2 Wk.                                                                             1 Mo.                                                                             2 Mo.                                     __________________________________________________________________________    43    --      85     15 5.2 4.8 5.3 --                                        44    B   5   80     15 10.3                                                                              9.7 9.3 9.5                                       45    B   6   79     15 11  10.5                                                                              10.5                                                                              11.5                                      46    B   10  75     15 15.2                                                                              16.3                                                                              16.6                                                                              16.5                                      47    B   15  70     15 23.9                                                                              25.7                                                                              25.2                                                                              27.1                                      48    C   4.5 80.5   15 11.2                                                                              11.1                                                                              10.9                                                                              11.3                                      49    C   5   80     15 12.1                                                                              12.9                                                                              12.1                                                                              --                                        50    C   10  75     15 17.6                                                                              17.6                                                                              16.6                                                                              --                                        51    C   15  70     15 29.5                                                                              29.1                                                                              30.8                                                                              --                                        52    D   2.0 83     15 9.1 --  9.5 9.3                                       53    D   4.0 81     15 10.1                                                                              --  10.1                                                                              10.6                                      54    D   6.0 79     15 10.7                                                                              --  10.9                                                                              11.3                                      55    D   8.0 77     15 12.9                                                                              --  13.3                                                                              14.3                                      56    --      91     9  7.3 6.9 7.0 --                                        57    B   5   86     9  10.9                                                                              10.7                                                                              12.6                                                                              11.6                                      58    B   5   86     9  11.5                                                                              11.2                                                                              11.6                                                                              12.3                                      59    B   10  81     9  19.4                                                                              18.1                                                                              18.1                                                                              18.8                                      60    B   15  76     9  27.7                                                                              27.2                                                                              26.3                                                                              26.8                                      61    C   3.5 87.5   9  10.7                                                                              11.7                                                                              11.5                                                                              11.8                                      62    C   3   88     9  10.5                                                                              11.6                                                                              12.4                                                                              --                                        63    C   8   83     9  15.8                                                                              16.5                                                                              16.2                                                                              --                                        64    B   2   92     6  9.3 10.1                                                                              9.0 9.1                                       65    B   4   90     6  10.4                                                                              11.6                                                                              11.2                                                                              10.5                                      66    B   6   88     6  13.6                                                                              13.1                                                                              13.3                                                                              13.2                                      67    C   2   92     6  8.7 9.5 8.3 9.0                                       68    C   4   90     6  11.5                                                                              12.2                                                                              11.9                                                                              11.7                                      69    C   6   88     6  13.1                                                                              14.1                                                                              13.4                                                                              14.0                                      __________________________________________________________________________

Table VI presents data correlating the melt index of lower MIcopolymers, outside the scope of the invention, with the melt indexstability of the blends. All the blends were prepared on the HaakeSystem 40 Mixer at 280° C. All the copolymers in this table had MI'sbetween 1000 and 2400 dg/min but this still was not high enough foroptimum effectiveness. It can be seen, for example, that while the MI'swere reasonably stable, increasing the amount of the high MI copolymerdid not in most cases significantly increase the MI of the blend.

                                      TABLE VI                                    __________________________________________________________________________    STABILIZATION OF MELT INDEX WITH HIGH MI COPOLYMERS                           High MI       Matrix      MI                                                  Sample No.                                                                          Copolymer, %                                                                          Polymer, %                                                                           % TiO.sub.2                                                                        Initial                                                                           2 Wk.                                                                             1 Mo.                                       __________________________________________________________________________    70    H   6   I  79  15   5.0 5.5 5.8                                         71    H   9   I  76  15   5.6 6.3 5.9                                         72    H   12  I  73  15   5.7 5.8 6.4                                         73    H   4   II 81  15   8.4 9.0 8.5                                         74    H   8   II 77  15   8.1 8.3 8.7                                         75    H   12  II 73  15   7.9 8.1 8.3                                         76    J   3   I  82  15   4.4 4.1 4.6                                         77    J   6   I  79  15   5.1 6.0 5.1                                         78    J   9   I  76  15   4.9 6.0 5.4                                         79    J   12  I  73  15   5.1 5.7 5.3                                         80    J   4   II 81  15   8.1 8.3 8.6                                         81    J   8   II 77  15   8.2 8.4 8.6                                         82    J   12  II 73  15   8.3 8.5 8.8                                         83    K   3   I  82  15   5.5 4.3 6.0                                         84    K   6   I  79  15   3.7 5.8 6.1                                         85    K   9   I  76  15   4.9 4.7 6.3                                         86    K   12  I  73  15   4.8 4.2 4.9                                         87    K   4   II 81  15   8.0 7.7 7.5                                         88    K   8   II 77  15   6.7 7.5 7.1                                         89    K   12  II 73  15   9.2 8.3 9.1                                         90    L   3   I  82  15   5.7 4.8 5.7                                         91    L   6   I  79  15   6.5 7.4 7.4                                         92    L   9   I  76  15   7.6 8.7 8.7                                         93    L   12  I  73  15   8.4 8.6 9.6                                         94    L   4   II 81  15   9.7 9.5 9.9                                         95    L   8   II 77  15   10.4                                                                              10.7                                                                              11.2                                        96    L   12  II 73  15   14.5                                                                              16.1                                                                              14.3                                        97    M   3   I  82  15   4.3 5.0 3.8                                         98    M   6   I  79  15   6.2 6.1 7.0                                         99    M   9   I  76  15   7.7 7.7 7.5                                         100   M   12  I  73  15   7.7 10.1                                                                              11.8                                        101   M   4   II 81  15   9.1 9.5 10.0                                        102   M   8   II 77  15   10.7                                                                              11.1                                                                              10.8                                        103   M   12  II 73  15   13.9                                                                              14.5                                                                              13.9                                        104   N   3   I  82  15   5.1 5.5 5.7                                         105   N   6   I  79  15   5.9 6.2 7.1                                         106   N   9   I  76  15   7.2 8.3 5.7                                         107   N   12  I  73  15   6.1 8.0 7.0                                         108   N   4   II 81  15   9.5 8.9 8.9                                         109   N   8   II 77  15   10.9                                                                              11.8                                                                              10.5                                        110   N   12  II 73  15   13.9                                                                              12.7                                                                              12.1                                        __________________________________________________________________________

Table VII presents similar data as Table VI, except that all the high MIcopolymers have MIs of at least 10,000. In this case, both high MIs andhigh MI stabilities are obtained for the blends; and, further, increaseof the level of high MI copolymer considerably increases the MI of theresulting blend. For example, sample 113 in this table was of the samecomposition as sample 92 in Table VI. Yet, at same level of high MIcopolymer, the blend MI in the former case was 10.2, but in the lattercase it was only 7.6.

                                      TABLE VII                                   __________________________________________________________________________    STABILIZATION OF MELT INDEX WITH HIGH MI COPOLYMERS                           High MI       Matrix      MI                                                  Sample No.                                                                          Copolymer, %                                                                          Polymer, %                                                                           % TiO.sub.2                                                                        Init.                                                                            2 Wk.                                                                             1 Mo.                                                                             2 Mo.                                    __________________________________________________________________________    111   E   3   I  82  15   3.7                                                                              3.0 2.6 2.9                                      112   E   6   I  79  15   6.4                                                                              7.1 6.4 5.3                                      113   E   9   I  76  15   10.2                                                                             10.8                                                                              8.8 10.2                                     114   E   12  I  73  15   13.5                                                                             14.4                                                                              13.5                                                                              14.4                                     115   E   4   II 81  15   12.1                                                                             12.7                                                                              11.7                                                                              11.2                                     116   E   8   II 77  15   14.6                                                                             14.2                                                                              12.9                                                                              13.7                                     117   E   12  II 73  15   21.0                                                                             21.2                                                                              20.4                                                                              19.9                                     118   F   3   I  82  15   2.3                                                                              3.9 2.6 --                                       119   F   6   I  79  15   5.6                                                                              5.9 7.5 --                                       120   F   9   I  76  15   9.0                                                                              9.1 10.2                                                                              --                                       121   F   12  I  73  15   12.0                                                                             12.4                                                                              12.3                                                                              --                                       122   F   4   II 81  15   11.1                                                                             10.9                                                                              10.2                                                                              --                                       123   F   8   II 77  15   14.0                                                                             13.4                                                                              13.3                                                                              --                                       124   F   12  II 73  15   17.6                                                                             18.0                                                                              18.7                                                                              --                                       125   G   3   I  82  15   3.0                                                                              4.9 5.2 --                                       126   G   6   I  79  15   6.4                                                                              7.8 7.4 --                                       127   G   9   I  76  15   8.4                                                                              9.6 7.6 --                                       128   G   12  I  73  15   11.2                                                                             11.7                                                                              12.4                                                                              --                                       129   G   4   II 81  15   9.7                                                                              10.3                                                                              10.2                                                                              --                                       130   G   8   II 77  15   13.5                                                                             13.2                                                                              14.1                                                                              --                                       131   G   12  II 73  15   16.5                                                                             17.2                                                                              17.3                                                                              --                                       __________________________________________________________________________

Table VIII summarizes the preparation of TiO₂ concentrates for thepractice of this invention.

Samples 132-138 were prepared using the Haake System 40 Mixer. Thosecompositions were then scaled up on a 30 mm twin screw extruder.Comparison of the initial MIs of samples 132 and 139 and samples 133 and140 shows good initial MI reproducibility on scale-up.

                                      TABLE VIII                                  __________________________________________________________________________    PIGMENTED COMPOSITIONS PREPARED USING CONCENTRATES                            PART A                                                                        Blended in the Haake Mixer                                                          High MI Matrix      Melt                                                                              Initial                                         Sample No.                                                                          copolymer, %                                                                          Polymer, %                                                                           TiO.sub.2, %                                                                       Temp.                                                                             Melt Index                                      __________________________________________________________________________    Blended in the Haake Mixer                                                    132   C   35.0                                                                              I  15  50   200 427                                             133   C   21.7                                                                              I  48.3                                                                              30   170 55                                              134   B   50.0                                                                              --     50   170 --                                              135   C   30.0                                                                              II 20  50   170 836                                             136   C   11.7                                                                              II 58.3                                                                              30   170 25                                              137   B   20.0                                                                              II 30  50   170 47                                              138   B   16.7                                                                              II 53.3                                                                              30   170 30                                              Extruded on 30 mm twin screw extruder                                         139   C   35.0                                                                              I  15  50   170 650   same as 132                               140   C   21.7                                                                              I  48.3                                                                              30   170 57    same as 133                               141   B   50.0                                                                              --     50   170 too liquid                                                                          to be extruded,                                                               same as 134                               142   C   16.7                                                                              II 33.3                                                                              50   170 86    --                                        143   C   11.7                                                                              II 58.3                                                                              30   170 22    same as 136                               144   B   20.0                                                                              II 30  50   170 27    same as 137                               145   B   16.7                                                                              II 53.3                                                                              30   170 30    same as 138                               __________________________________________________________________________

Table IX is a continuation of the experiments reported in Table VIII.All the compositions were compounded using a Haake System 40 Mixer.Table IX demonstrates that the invention can be practiced in two steps,using Ti02 concentrates, to the same extent as by blending individualcomponents in a one-step operation. The concentrates were blended witheither Matrix Polymer I or Matrix Polymer II in such amounts that theresulting blends contained either 9% or 15% of TiO₂. The initial MIs ofthe final blends were comparable to those of the correspondingsingle-step preparations, which MIs are given in square brackets.

                                      TABLE IX                                    __________________________________________________________________________    PIGMENTED COMPOSITIONS PREPARED USING CONCENTRATES                            PART B                                                                        Concentrate   Matrix Melt                                                                              Melt Index                                           Sample No.                                                                          Sample No., %                                                                         Polymer, %                                                                           Temp                                                                              Init.* 2 Wk.                                                                             1 Mo.                                                                             2 Mo                                  __________________________________________________________________________    146   132 30  I  70  280 10.3   10.1                                                                              8.8 10.3                                                           [9.2]                                                Gives 10.5% High MI Copolymer C + 74.5% Matrix Copolymer I + 15%              TiO.sub.2                                                                     147   133 30  I  70  280 8.4    9.5 8.1 9.5                                                            [8.2]                                                Gives 6.5% High MI Copolymer C + 84.5% Matrix Copolymer I + 9% TiO.sub.2      148   134 30  I  70  280 9.8    10.0                                                                              9.0 9.2                                                            [8.3]                                                Gives 15% High MI Copolymer B + 70% Matrix Copolymer I + 15% TiO.sub.2        149   135 30  II 70  280 15.5   17.1                                                                              16.1                                                                              16.4                                  Gives 9% High MI Copolymer C + 76% Matrix Copolymer II + 15% TiO.sub.2        150   136 30  II 70  280 12.4   12.9                                                                              12.5                                                                              12.5                                                           [10.7]                                               Gives 3.5% High MI Copolymer C + 87.5% Matrix Copolymer II + 9%               TiO.sub.2                                                                     151   137 30  II 70  280 8.9    9.7 11.0                                                                              9.8                                                            [11.0]                                               Gives 6% High MI Copolymer B + 79% Matrix Copolymer II + 15% TiO.sub.2        152   138 30  II 70  280 12.5   13.5                                                                              13.5                                                                              11.9                                                           [8.1]                                                Gives 5% High MI Copolymer B + 86% Matrix Copolymer II + 9% TiO.sub.2         153   139 30  I  70  280 8.0    9.0 --  9.0                                                            [10.3]                                               Gives 10.5% High MI Copolymer C + 74.5% Matrix Copolymer I + 15%              TiO.sub.2                                                                     154   140,                                                                              30  I  70  280 5.8    7.1 --  7.8                                                            [8.4 for 147]                                        Gives 6.5% High MI Copolymer C" + 84.5% Matrix Copolymer I + 9%               TiO.sub.2                                                                     155   142 30  II 70  280 11.4   12.5                                                                              --  12.3                                  Gives 5% High MI Copolymer C + 80% Matrix Copolymer II + 15% TiO.sub.2        156   143 30  II 70  280 10.4   9.6 --  11.2                                                           [12.4]                                               Gives 3.5% High MI Copolymer C + 87.5% Matrix Copolymer II + 9%               TiO.sub.2                                                                     157   144 30  II 70  280 10.4   11.4                                                                              --  11.1                                                           [8.9]                                                Gives 6% High MI Copolymer B + 79% Matrix Copolymer II + 15% TiO.sub.2        158   145 30  II 70  280 11.9   10.1                                                                              --  12.3                                                           [12.5]                                               Gives 5% High MI Copolymer B + 86% Matrix Copolymer II + 9%                   __________________________________________________________________________    TiO.sub.2                                                                      *Number in square brackets is the MI of the corresponding blend prepared      from the same components in one step, without using a concentrate        

LAMINATION EXPERIMENTS

In the following experiments, all data obtained in units other than SIhave been converted to SI units.

Adhesive strength of laminates was determined according to the followingtest (with indicated variants).

A specimen, 2.54 cm wide and 12.7 cm long (in Example 1) or 15 mm wideand 25.4 cm long (in Example 2) was used for the test. About 2.5 cm ofthe coating was manually peeled from the substrate. The coating wasplaced in the upper jaw of the Instron Tensile Tester (in Example 1) orof the Zwick Model 1410 testing machine (in Example 2), and thesubstrate was placed in the lower jaw. The specimen was peeled at a 90°angle either at a crosshead speed of 30.5 cm per minute (in Example 1)or of 10 cm per minute (in Example 2). The load required to peel thecoating away from the substrate was measured in units of force (orweight) per unit of width. In each test, triplicate measurements weremade, and the average result was reported.

EXAMPLE 1

Two compositions, designated respectively as Compound 1A and Compound1B, were compounded as follows:

    ______________________________________                                        Compound 1A                                                                   E/MAA copolymer II from Table II (matrix)                                                               81.5%                                               TiO.sub.2 (Ti-Pure ® R101)                                                                          12.5%                                               E/AA copolymer B from Table III (high MI)                                                               6.0%                                                Compound 1B                                                                   E/MAA copolymer I from Table II (matrix)                                                                75.0%                                               TiO.sub.2 (Ti-Pure ® R101)                                                                          15.0%                                               E/AA copolymer C from Table III (high MI)                                                               10.0%                                               ______________________________________                                    

These compounds were extruded and laminated onto untreated 51 micrometerthick aluminum foil using an 11.4 cm Egan Laminator Coater®. Theextruder was fitted with a two-stage mixing screw having alength-to-diameter (L/D) ratio of 28:1 and a compression ratio of 5:1.The extruder temperature settings were 177-304° C., the polymer melttemperature being 285-305° C. Each compound was extruded through a 122cm wide ER-WA-PA® coat hanger die with a 508 micrometer opening. Theextruded polymer film was laminated to the aluminum foil substrate usinga matte finish chill roll. Line speed determined the ultimate coatingthickness. The laminates were stored at ambient temperature for either13 days or 57 days. The adhesive strength of the pigmented material wasmeasured using the 90 peel test. The results are given below in Table X.

                  TABLE X                                                         ______________________________________                                               Line     Coating     Adhesive                                                                              Adhesive                                  Compd. Speed    Thickness   Str., g/cm                                                                            Str., g/cm                                (Sample)                                                                             m/min    micrometers 13 days 57 days                                   ______________________________________                                        1A   (1)   40.2     76        189     351                                     1A   (2)   61.0     51        552     465                                     1A   (3)   121.6    25        240     236                                     1B   (4)   40.5     76        193     311                                     1B   (5)   60.6     51        213     410                                     1B   (6)   121.9    25        221     236                                     ______________________________________                                    

EXAMPLE 2

A white-pigmented composition was compounded as follows:

    ______________________________________                                        E/MAA 96:4 copolymer, MI = 7 (matrix)                                                                  84.0%                                                TiO.sub.2 (Ti-Pure ® R101)                                                                         9.0%                                                 E/AA copolymer B, Table III (high MI)                                                                  7.0%                                                 ______________________________________                                    

The laminates were prepared using a 9 cm Egan Laminator Coater® (mixingscrew of L/D ratio of 30:1) with temperature settings of 170° C., 210°C., 250° C., 270° C., and 290° C. for the barrel and 290° C. for theconnecting pipes. The air gap was 15 cm. The die opening was 700micrometers and the die width 80 cm. Films were cast using a semi-mattefinish chill roll. Aluminum foil and clear LDPE films were used assubstrates for the laminated structures. In Test 2, below, (withmultilayer laminates), two inner adhesive layers were formed by anunpigmented E/AA copolymer (9% AA, MI=10).

TEST 1

LDPE film//WPAC//E/AA copolymer//aluminum foil. This was the bottomportion of the multilayer laminate of Test 2.

TEST 2

The laminate from Test 1 was passed through the laminating line for thesecond time to give the following structure (from bottom to top): LDPEfilm//WPAC//E/AA copolymer//aluminum foil//E/AA copolymer//WPAC//LDPEfilm

The adhesive strength of 15 mm-wide test strips was determined in the90° peel test. The average adhesion strength, in N/15 mm, was asfollows:

    ______________________________________                                        For LDPE film//WPAC (bottom layer)                                                                     7.4                                                  For WPAC//LDPE film (top layer)                                                                        13.6                                                 ______________________________________                                    

I claim:
 1. A laminated structure comprising at least one nonadhesivelayer and at least one white-pigmented adhesive layer, in which thewhite-pigmented adhesive layer is made of a composition stabilizedagainst thermal crosslinking and consequent reduction of its melt index,consisting essentially of a uniform dispersion of alumina-coatedtitanium dioxide pigment in a blend of a matrix polymer with astabilizing polymer,the matrix polymer being a copolymer represented bythe formula E/X/Y, where E stands for ethylene; X stands for a C₃ -C₇alpha, beta-unsaturated carboxylic acid; and Y, which is optional,stands for another copolymerizable comonomer selected from the groupconsisting of C₃ -C₇ alpha, beta-unsaturated carboxylic acids, C₁ -C₁₀alkyl esters of such acids, vinyl esters, vinyl ethers, acrylonitrile,methacrylonitrile, carbon monoxide, and sulfur dioxide; the respectiverelative weight ratios of the monomers in said E/X/Y copolymer beingabout 96:4:0 to 40:30:30, and the melt index of said copolymer,determined according to ASTM D1238, Condition E, being about 0.1-100dg/min; and the stabilizing polymer being a high melt index copolymer ofethylene with an unsaturated carboxylic acid selected from the groupconsisting of acrylic acid (E/AA copolymer) and methacrylic acid (E/MAAcopolymer), said high melt index copolymer having a melt index of atleast about 5,000 dg/min, determined according to ASTM D1238, conditionE, and containing at least about 5 weight percent of carboxylic acidmonomer; the relative weight ratio of matrix polymer to stabilizingpolymer being about 95:5 to 80:20, and the amount of titanium dioxide inthe blend being about 5 to 20 weight percent.
 2. A laminated structureof claim 1 wherein the melt index of the high melt index copolymer is atleast 10,000 dg/min.
 3. A laminated structure of claim 1 wherein theamount of carboxylic acid monomer in the high melt index copolymer is atleast 9 weight percent.
 4. A laminated structure of claim 2 wherein theamount of carboxylic acid monomer in the high melt index copolymer is atleast 9 weight percent.
 5. A laminated structure of claim 1 wherein thestabilized composition is further compounded to incorporate minoramounts of one or more additives selected from the group consisting ofother stabilizers, antioxidants, and slip improving agents.
 6. Alaminated structure of claim 1 wherein the stabilized composition isadditionally formulated with one or more additives selected from thegroup consisting of plasticizers and fire retardants, the total amountof plasticizers, if present, being no more than about 15 weight percentof the final composition; and the amount of fire retardants, if present,being about 10 to 30 weight percent of the final composition.
 7. Alaminated structure of claim 1 wherein the E/X/Y copolymer is adipolymer of ethylene with methacrylic acid, wherein methacrylic acid ispresent in an amount of 3-30 weight percent, and Y is present in anamount of 0 weight percent.
 8. A laminated structure of claim 7 whereinthe amount of methacrylic acid in the E/X/Y copolymer is 4-15 weightpercent.
 9. A laminated structure of claim 2 wherein the E/X/Y copolymeris a dipolymer of ethylene with methacrylic acid, wherein methacrylicacid is present in an amount of 3-30 weight percent, and Y is present inan amount of 0 weight percent.
 10. A laminated structure of claim 9wherein the amount of methacrylic acid in the E/X/Y is 4-15 weightpercent.
 11. A laminated structure of claim 1 wherein the E/X/Ycopolymer is a dipolymer of ethylene with acrylic acid, wherein acrylicacid is present in an amount of 3-30 weight percent, and Y is present inan amount of 0 weight percent.
 12. A laminated structure of claim 1wherein the E/X/Y copolymer is a terpolymer of ethylene in which X ismethacrylic acid, and Y is selected from the group consisting of vinylacetate, n-butyl acrylate, and isobutyl acrylate.
 13. A laminatedstructure of claim 1 wherein the E/X/Y copolymer is a terpolymer ofethylene in which X is acrylic acid, and Y is selected from the groupconsisting of vinyl acetate, n-butyl acrylate, and isobutyl acrylate.14. A laminated structure of claim 1 wherein at least one nonadhesivelayer is selected from the group consisting of metal sheets and foils,plastic sheets and films, and kraft paper, and the at least onestabilized adhesive layer is positioned adjacent an outer layer, whichis made of clear plastic.
 15. A laminated structure of claim 14 whereinthe clear plastic is selected from the group consisting of polyester andlow density polyethylene.